Second-harmonic generation from complementary au metasurfaces with triangular resonators

We demonstrate the contribution of local electric near-field enhancement around convex and concave corners at resonant fundamental excitation to the second-harmonic (SH) emission intensity using complementary Au metasurfaces with triangular resonators (i.e., a square array of triangular particles and a square array of a thin film of Au with a triangular hole). It is demonstrated that for an electric near-field enhancement at normal incidence, the fundamental excitation around convex corners of a triangular particle is many times stronger than the one around concave corners of a complementary triangular hole. Notwithstanding, the SH emission intensity of the complementary structure is found to be comparable at their respective optimal resonant fundamental excitations. SH emission intensity is numerically estimated using mode overlap between the fundamental and SH waves. The comparable SH emission intensity is found to originate from the strong electric near-field enhancement on the sides of a triangular hole with zero curvature, which compensates for the field suppression around the concave corners of the triangular hole. In addition, the strong electric near-field enhancement around convex corners of a triangular particle (accompanied with suppression around the sides of the triangular particle) and field suppression around concave corners of a triangular hole (accompanied with strong field enhancement around the side of the triangular hole) are demonstrated using Babinet’s principle.